Any user can utilize an IP telephone system if he or she has installed, into a network terminal such as a personal computer or a telephone terminal, a conversation application, which is a software for transmitting, receiving calls and achieving telephone talks, provided by the IP telephone company. In the conversation application, there are registered user ID, display name and profile. Thus, the conversation application identifies the user by means of the user ID, display name and profile. An example of the IP telephone system is Skype (registered trademark).
Japanese Patent Application Publication No. 2003-169107 describes a system in which a personal computer, i.e., a network terminal capable of performing network communication, and a head-set, i.e., an interface device, are USB-connected and a conversation application is used to achieve IP telephone communication. The personal computer incorporates a switch that changes a signal outputting a call-arrival tone generating signal to the built-in speaker and a conversation signal to the head-set.
Japanese Patent Application Publication No. 2005-175722 discloses a system in which a personal computer, i.e., a network terminal capable of performing network communication, and a head-set, i.e., an interface device, are USB-connected. Any user who has a network terminal and uses a hand-set can have an IP telephone conversation with another user who has a device connected to a network, by using the conversation application installed in the network terminal.
The conversation application transmits and receives message data and audio data to and from the interface device. The message data is information that controls the interface device and achieves mail transmission and receipt. The audio data represents the content of conversation. In case that a plurality of interface devices are connected to the network terminal and that one of the interface devices has been designated, then both the message data and the audio data must be communicated between the conversation application and the designated interface device.
A configuration of a conventional IP telephone system is shown in FIG. 12. As shown in FIG. 12, the IP telephone system includes a network terminal 100 such as a personal computer, an interface device 102a such as a USB telephone or a USB facsimile, and an IP telephone terminal 103.
The network terminal 100 and the IP telephone terminal 103 are connected bi-directionally by way of a network 106. The network terminal 100 and the interface device 102a have one USB port respectively. The USB port of the terminal 100 and the USB port of the interface device 102a are connected, so that the network terminal 100 and the interface device 102a are connected to each other.
The interface device 102a has a speaker-microphone unit (not shown). The interface device 102a can input and output the sound. The interface device 102a can perform data communication with the network terminal 100 via the USB port.
The conversation application 150 and a cooperative application 151 will be operated in the network terminal 100. A device driver 152a and an audio driver 153a will be operated in association with the interface device 102a. The network terminal 100 has a speaker-microphone unit 154 that enables the network terminal 100 to input and output an audio data.
With the arrangement described above, the conventional IP telephone system can communicate with the IP telephone terminal 103 as described below. The conversation application 150 is the application software in order to enable the network terminal 100 and the interface device 102a to communicate with the IP telephone terminal 103 via the network 106. The conversation application 150 is, for example, Skype software sold by Skype Limited.
The conversation application 150 enables the user to select either the speaker-microphone unit 154 provided in the network terminal 100 or the speaker-microphone unit 154 provided in the interface device 102a for the purpose of communication with the IP telephone terminal 103. The conversation application 150 can exchange audio data AD with the speaker-microphone unit the user has selected, through the audio drivers 153a and 153b incorporated in the network terminal 100.
More specifically, the conversation application 150 outputs the audio data DA representing a call arrival from the IP telephone terminal 103 or the audio data AD representing a conversation speech transmitted from the IP telephone terminal 103 to the device driver 152a or 153b corresponding to the speaker the user has selected. Either the device driver 152a or the device driver 153b reproduces the audio data, which is supplied to the speaker. Herewith, the speaker generates the sound of the speech represented by the audio data. The conversational speech input to a microphone that the user has selected is converted to the audio data AD by means of the audio drivers 153a or 153b corresponding to the microphone. This audio data AD is input to the conversation application 150. Thus, the conversation application 150 transmits the audio data AD to the IP telephone terminal 103.
In the conventional IP telephone system described above, the speaker the user has selected outputs the sound of speech coming from the IP telephone terminal 103, and the user can be input conversational speeches to the IP telephone terminal 103 from the microphone the user has selected.
The conversation application 150 has the function of informing the user of a call arrival and acquiring the inputs from the user through the user interface such as the display and keyboard of the network terminal 100. Therefore, the user can receive the notification from the conversation application 150 during the conversation through the speaker-microphone unit of the network terminal 100 and can operate the conversation application 150.
The conversation application 150 is so described configured, enabling the user converse through the speaker-microphone unit of the network terminal 100. The interface device 102a is used as a speaker-microphone unit only, not as anything else.
The cooperative application 151 links the conversation application 150 and the interface device 102a to each other, and serves the interface device 102a as the user interface. Hence, the cooperative application 151 has the function of informing the call arrival from the conversation application 150 to the display provided in interface device 102a, and has the function of transmitting any user input by keys provided in interface device 102a to the conversation application 150.
The cooperative application 151 uses an application program interface (API), exchanging various messages with the conversation application 150, and exchanging information data DD, which contains various messages, with the interface device 102a through the device driver 152a. The various messages can therefore be exchanged between the conversation application 150 and the interface device 102a. 
Using the cooperative application 151, when the user uses the speaker-microphone unit of the interface device 102a, the user can receive notification from the conversation application 150 through the user interface of the interface device 102a and can operate the conversation application 150.
However, the conventional IP telephone system has following problems. Assume that the user, who usually uses the speaker-microphone unit of the network terminal 100 to converse through the IP telephone system, may use the interface device 102a (e.g., the extension of a USB main-extension phone, located far from the network terminal 100). In this case, the user input is transmitted from the interface device 102a to the conversation application 150. The conversation application 150 can therefore start communicating with the IP telephone terminal 103. However, the conversational speech that the conversation application 150 has received from the IP telephone terminal 103 is reproduced by the speaker provided in the network terminal 100. Thus, the user, who is using the interface device 102a, cannot perform conversation.
That is, the device (network terminal 100 or interface device 102a) having the speaker-microphone unit set by the conversation application 150 is not always corresponding to the device having the user interface actually used to achieve conversation. Here arises a problem.
The system disclosed in Japanese Patent Application Publication No. 2003-169107 has a switch as illustrated in FIGS. 1 and 2 of the publication. The user may operate the switch to supply the call-arrival tone generating signal received via a network, either to the speaker incorporated in the network terminal or to the speaker of the head set connected to the network terminal. However, the publication does not disclose a configuration in which the head set is used as a user interface that gives gives the user the notification coming from the conversation application or receives inputs the user has made.
In other words, Japanese Patent Application Publication No. 2003-169107 does not disclose that audio data may be switched between the interface devices connected to the network terminals provided in the system. Consequently, the problem pointed out above arises. That is, the user using one of the interface devices cannot converse with anyone else who uses another interface device that is receiving audio data.
In the system disclosed in Japanese Patent Application Publication No. 2003-169107, the network terminal must be customized to be an IP telephone terminal to have a switch dedicated for receiving audio data. If provided with this switch, however, the customized network terminal can no longer be used as ordinary network terminal, having but lower versatility.
Japanese Patent Application Publication No. 2005-175722 does not disclose the technique of first selecting one of interface devices and then exchanging message data and audio data between the conversation application and the interface device selected. The audio data may not be transmitted to or received between the conversation application and the interface device, though the message data can be transmitted and received therebetween. In this case, when a call request comes from an external IP telephone terminal connected to the network, the call-notifying message can indeed be transmitted to the interface device, but the audio data representing the call-arrival tone cannot be transmitted. This is a problem. Further, even if the user uses the interface device, responding to the call request, the audio data representing the conversation cannot be exchanged between the user and the external IP telephone terminal. This is another problem. Conversely, the user may request for conversation with another user of the external IP telephone terminal through the conversation application, by using the interface device. In this case, the audio data representing the conversation cannot be exchanged between the interface device and the external IP telephone terminal. This is still another problem.
Japanese Patent Application Publication No. 2005-175722 discloses a configuration in which a USB cable connects the PC to the main-extension phone, enabling the user to use the main-extension phone, thereby to converse with another user of an IP telephone terminal connected to the network. However, the publication dose not disclose any arrangement for solving the problem that the device having a speaker-microphone unit set in the conversation application is not always compatible with the device having the user interface actually used to accomplish conversation.